Οργανωμένες πορώδεις δομές από νανοκρυστάλλους οξειδίου μετάλλου: σύνθεση, δομικός χαρακτηρισμός και εφαρμογές στην οξειδοαναγωγική κατάλυση

The rapid development of civilization and industrial activities has led to a large amount of pollutants being disposed into the environment either intentionally or accidentally, including toxic metals with great health concerns. Chromium is a heavy metal with variable oxidation states; in aquatic systems, chromium exists mostly in the hexavalent (Cr(VI)) and trivalent (Cr(III)) forms. Anionic Cr(VI) species are far more mobile and toxic than Cr(III) and difficult to remove from water. The World Health Organization (WHO) recommended a maximum allowable concentration of 50 μg/L for Cr(VI) in drinking water. Moreover, as a consequence of its toxicity, Cr(VI) has also been categorized as a Group I human carcinogen by the International Agency for Research on Cancer (IARC). Therefore, finding an effective way for remediation of Cr(VI)-contaminated solutions is undoubted of high priority in the field of environmental and health protection.This dissertation focuses on synthesis, structural characterization and environmental applications of high-surface-area mesoscopic architectures composed of tightly connected ultra-small metal oxide nanoparticles. In particular, we found that mesoporous spinel ferrite nanoparticle assemblies (MeFe2O4 or MeFO MNAs, Me = Zn, Mn, Ni, Cd and Co) can efficiently suppress electron-hole recombination, manifesting an exceptional activity and magnetic recyclability in photocatalytic reduction of aqueous Cr(VI). Among spinel ferrite nanocrystal assemblies, ZFO MNAs present the highest activity which is a result of the combined effect of accessible pore surface area (ca. 105–159 m2/g), appropriate band edge positions and small grain composition (ca. 6–7 nm in size). Moreover, in an effort to further improve the photocatalytic performance of ZFO assemblies, we suggest the synthesis of new binary mesoporous networks consisting of ZFO and MFO (x% MFO-ZFO MNAs, x = 4–12.5 wt%) nanoparticles as promising catalysts for detoxification of Cr(VI) aqueous solutions. The remarkable activity and durability of the 6.5% MFO-ZFO MNAs implies the great possibility of implementing these new composite catalysts into a realistic Cr(VI) detoxification of contaminated water. Additional subject of the present doctoral thesis is the synthesis of mesoporous Mn3O4 nanoparticle assemblies and investigation of their catalytic activity in oxo-functionalization of various aromatic and cyclic alkenes as well as aryl alkanes with tert-butyl hydroperoxide (TBHP) as mild oxidant. The successful synthesis of this material highlights the general applicability of the proposed polymer-assisted aggregating self-assembly method to produce high-surface-area mesoporous networks of cross-linked metal oxide nanoparticles. Through comparative studies, we evidenced that the high catalytic activity and stability of these Mn3O4 assemblies arise from the unique 3D open-pore structure, large internal surface area (ca. 90 m2/g) and uniform pores (ca. 6.6 in size). These results open up the possibility of using mesoporous assembled structures of small-sized Mn3O4 nanocrystals for selective alkene and aryl alkane oxidations.Η ταχεία πολιτισμική ανάπτυξη καθώς και η ανέλιξη των βιομηχανικών δραστηριοτήτων έχει οδηγήσει στην απόρριψη μεγάλων ποσοτήτων ρύπων στο περιβάλλον, είτε σκόπιμα είτε εξ αμελείας, συμπεριλαμβανομένων τοξικών μετάλλων που δημιουργούν μεγάλη ανησυχία για την υγεία. Το χρώμιο είναι ένα βαρύ μέταλλο με ποικίλες οξειδωτικές καταστάσεις. Στα υδρόβια συστήματα, το χρώμιο υπάρχει κυρίως στην εξασθενή (Cr(VI)) και τρισθενή (Cr(III)) μορφή του. Τα ανιονικά είδη Cr(VI) είναι πολύ πιο ευκίνητα και τοξικά από το Cr(III) με αποτέλεσμα τη δυσκολία απομάκρυνσής τους από το νερό. Ο Παγκόσμιος Οργανισμός Υγείας (ΠΟΥ) συστήνει ως μέγιστη επιτρεπόμενη συγκέντρωση τα 50 μg/L για το Cr(VI) στο πόσιμο νερό. Επιπλέον, ως συνέπεια της τοξικότητάς του, το Cr(VI) έχει χαρακτηριστεί ως καρκινογόνος παράγοντας της ομάδας Ι από τον Διεθνή Οργανισμό Έρευνας για τον Καρκίνο (IARC). Επομένως, η εύρεση ενός αποτελεσματικού τρόπου για την αποκατάσταση των μολυσμένων με Cr(VI) διαλυμάτων αποτελεί αναμφίβολα υψηλή προτεραιότητα στον τομέα της προστασίας του περιβάλλοντος και της υγείας. Η παρούσα διατριβή εστιάζει στη σύνθεση, τον δομικό χαρακτηρισμό και τις περιβαλλοντικές εφαρμογές μεσοπορωδών πλεγμάτων υψηλής επιφάνειας που αποτελούνται από διασυνδεδεμένα μεταξύ τους νανοσωματίδια οξειδίου μετάλλου. Συγκεκριμένα, βρήκαμε ότι μεσοπορώδεις δομές νανοσωματιδίων με δομή σπινελίου φερρίτη (MeFe2O4 ή MeFO MNAs, όπου Me = Zn, Mn, Ni, Cd και Co) μπορούν αποτελεσματικά να καταστείλλουν την επανασύνδεση οπής-ηλεκτρονίου, επιδεικνύοντας μια εξαιρετική δραστικότητα και μαγνητική ανακυκλωσιμότητα στη φωτοκαταλυτική αναγωγή υδατικού διαλύματος Cr(VI). Μεταξύ των μεσοπορωδών πλεγμάτων με δομή σπινελίου φερρίτη, οι μεσοδομές ZFO παρουσιάζουν την υψηλότερη δραστικότητα ως αποτέλεσμα της προσβάσιμης επιφάνειας πόρων (~105–159 m2/g), των κατάλληλων ενεργειακών ζωνών και του μικρού μεγέθους νανοκρυστάλλων (~6–7 nm). Επιπλέον, σε μια προσπάθεια περαιτέρω βελτίωσης της φωτοκαταλυτικής απόδοσης των μεσοπορωδών ZFO πλεγμάτων, προτείνουμε τη σύνθεση νέων σύνθετων μεσοπορωδών πλεγμάτων που αποτελούνται από νανοσωματίδια ZFO και MFO (x% MFO-ZFO MNAs, x=4–12,5 wt%) ως υποσχόμενους καταλύτες για την απορρύπανση υδατικών διαλυμάτων Cr(VI). Η αξιοσημείωτη δραστικότητα και αντοχή των μεσοδομών 6,5% MFO-ZFO συνεπάγεται την δυνατότητα ευρείας εφαρμογής αυτών των νέων σύνθετων καταλυτών στην απορρύπανση μολυσμένου με Cr (VI) νερού σε πραγματικό περιβάλλον. Επιπρόσθετο αντικείμενο της παρούσας διδακτορικής διατριβής είναι η σύνθεση μεσοπορωδών πλεγμάτων απο νανοσωματίδια Mn3O4 και η διερεύνηση της καταλυτικής τους δραστικότητας στην οξείδωση διαφόρων αρωματικών και κυκλικών αλκενίων καθώς και άρυλο-αλκανίων χρησιμοποιώντας υπεροξείδιο του τριτοταγούς βουτυλίου (TBHP) ως ήπιο οξειδωτικό. Η επιτυχής σύνθεση του παραπάνου υλικού υποδηλώνει τη γενική εφαρμοσιμότητα της προτεινόμενης μεθόδου αυτοσυναρμολόγησης με τη βοήθεια πολυμερών για την ανάπτυξη μεσοπορωδών δικτύων υψηλής επιφάνειας από διασυνδεδεμένα νανοσωματίδια οξειδίου μετάλλου. Μέσω συγκριτικών μελετών, αποδεικνύουμε ότι η υψηλή καταλυτική δραστικότητα και σταθερότητα των πλεγμάτων Mn3O4 προκύπτει από τη μοναδική 3D δομή τους, την μεγάλη εσωτερική επιφάνεια (~90 m2/g) και τους ομοιόμορφους πόρους (~6,6 σε μέγεθος). Αυτά τα αποτελέσματα διευρύνουν τη δυνατότητα χρήσης μεσοπορώδων πλεγμάτων από μικρού μεγέθους νανοκρυστάλλους Mn3O4 για επιλεκτική οξείδωση αλκενίων και άρυλο-αλκανίων

Mesoporous Composite Networks of Linked MnFe2O4 and ZnFe2O4 Nanoparticles as Efficient Photocatalysts for the Reduction of Cr(VI)

Semiconductor photocatalysis has recently emerged as an effective and eco-friendly approach that could meet the stringent requirements for sustainable environmental remediation. To this end, the fabrication of novel photocatalysts with unique electrochemical properties and high catalytic efficiency is of utmost importance and requires adequate attention. In this work, dual component mesoporous frameworks of spinel ferrite ZnFe2O4 (ZFO) and MnFe2O4 (MFO) nanoparticles are reported as efficient photocatalysts for detoxification of hexavalent chromium (Cr(VI)) and organic pollutants. The as-prepared materials, which are synthesized via a polymer-templated aggregating self-assembly method, consist of a continuous network of linked nanoparticles (ca. 6–7 nm) and exhibit large surface area (up to 91 m2 g−1 ) arising from interstitial voids between the nanoparticles, according to electron microscopy and N2 physisorption measurements. By tuning the composition, MFO-ZFO composite catalyst containing 6 wt.% MFO attains excellent photocatalytic Cr(VI) reduction activity in the presence of phenol. In-depth studies with UV-visible absorption, electrochemical and photoelectrochemical measurements show that the performance enhancement of this catalyst predominantly arises from the suitable band edge positions of constituent nanoparticles that efficiently separates and transports the charge carriers through the interface of the ZFO/MFO junctions. Besides, the open pore structure and large surface area of these ensembled networks also boost the reaction kinetics. The remarkable activity and durability of the MFO-ZFO heterostructures implies the great possibility of implementing these new nanocomposite catalysts into a realistic Cr(VI) detoxification of contaminated wastewater

Assembly and photochemical properties of mesoporous networks of spinel ferrite nanoparticles for environmental photocatalytic remediation

Spinel ferrite materials have an electronic band structure that is well suited for visible light-induced catalysis, however, their photocatalytic activity remains low due to the daunting charge-carrier separation process. In this article, we report that high-surface-area mesoscopic architectures composed of tightly connected ultrasmall spinel ferrite nanocrystals can efficiently suppress electron-hole recombination, manifesting an exceptional activity and magnetic recyclability in photocatalytic reduction of aqueous Cr(VI). Revealed by electron microscopy, N2 physisorption, and X-ray scattering studies, the resulting materials, which were obtained through a block copolymer-assisted cross-linking aggregation of colloidal nanoparticles, show a 3D interconnected nanoporous structure with a large internal surface area (up to 159 m2 g−1) and exhibit small grain composition (ca. 6–8 nm in size). Through a systematic synthesis of various structural analogues to the spinel ferrite family and optical absorption and electrochemical impedance spectroscopy analyses, we demonstrate that the electronic band structure fits the electronic requirements for both Cr(VI) reduction and water oxidation under UV–vis light irradiation. Among spinel ferrites, ZnFe2O4 presents the highest activity, readily operating without additional sacrificial reagents in photocatalytic detoxification of aqueous Cr(VI), which together with transient gas analysis and fluorescence spectroscopy results suggest a competitive formation of oxygen and hydroxyl radicals at the catalyst surface. These findings provide an essential tool for the delineation of the electronic structure-catalytic property relationship in spinel ferrite nanostructures offering intriguing possibilities for designing new photocatalytic systems for efficient environmental pollution purification and energy conversion

Assembly and photochemical properties of mesoporous networks of spinel ferrite nanoparticles for environmental photocatalytic remediation

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Replication protein A is an independent prognostic indicator with potential therapeutic implications in colon cancer

Replication protein A (RPA), a component of the origin recognition complex, is required for stabilization of single-stranded DNA at early and later stages of DNA replication being thus critical for eukaryotic DNA replication. Experimental studies in colon cancer cell lines have shown that RPA protein may be the target of cytotoxins designed to inhibit cellular proliferation. This is the first study to investigate the expression of RPA1 and RPA2 subunits of RPA protein and assess their prognostic value in colon cancer patients. We analyzed immunohistochemically the expression of RPA1 and RPA2 proteins in a series of 130 colon cancer resection specimens in relation to conventional clinicopathological parameters and patients' survival. Statistical significant positive associations emerged between: (a) RPA1 and RPA2 protein expressions (P=0.0001), (b) RPA1 and RPA2 labelling indices (LIs) and advanced stage of the disease (P=0.001 and 0.003, respectively), (c) RPA1 and RPA2 LIs and the presence of lymph node metastasis (P=0.002 and 0.004, respectively), (d) RPA1 LI and the number of infiltrated lymph nodes (P=0.021), (e) RPA2 LI and histological grade of carcinomas (P=0.05). Moreover, a statistical significant higher RPA1 LI was observed in the metastatic sites compared to the original ones (P=0.012). RPA1 and RPA2 protein expression associated with adverse patients' outcome in both univariate (log rank test: P<0.00001 and 0.00001, respectively) and multivariate (Cox model: P=0.092 and 0.0001, respectively) statistical analysis. Statistical significant differences according to the expression of RPA1 and RPA2 proteins were also noticed in the survival of stage II (P<0.00001 and 0.0016, respectively) and stage III (P=0.0029 and 0.0079, respectively) patients. In conclusion, RPA1 and RPA2 proteins appear to be useful prognostic indicators in colon cancer patients and attractive therapeutic targets for regulation by tumor suppressors or other proteins involved in the control of cell proliferation. © 2007 USCAP, Inc All rights reserved

A microporous Mg2+ MOF with cation exchange properties in a single-crystal-to-single-crystal fashion

We report herein a new alkaline earth metal ion organic framework [Mg-2(NH2BDC)(2)(HNO3)]center dot 9H(2)O (AEMOF-7), which shows a 3-D microporous structure with several unusual features, such as the rare trigonal prismatic coordination geometry of one of the crystallographically unique Mg-2(+) centers and the existence of a bridging HNO3 ligand. The H+ ions of the HNO3 ligand are dissociable as demonstrated via proton conductivity measurements. AEMOF-7 displays relatively high selectivity for CO2 vs. CH4 and negligible N-2 uptake. Interestingly, this compound was found to be capable of single-crystal-to-single-crystal (SCSC) exchange of Mg2+ by Cu2+ ions, which was observed for the first time in a MOF material. AEMOF-7 is also luminescent and its photophysical properties were investigated via solid state UV-Vis, steady-state and time-resolved luminescence studies